CBC · California Building Code

How are deep foundations (piles, drilled shafts) analyzed, designed and detailed?

Under the California Building Code, piles and drilled shafts must be designed from a soils report, checked for axial and lateral capacity (by calculation or load test), sized and detailed to the §1810 rules (including minimum diameters, length limits, group effects and seismic detailing), and verified by the specified tests when the code requires them.

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Last reviewed: July 5, 2026

What the code requires — in plain English

The California Building Code (CBC) requires deep foundations (piles, drilled shafts, micropiles, etc.) to be analyzed, designed, detailed and installed based on an appropriate geotechnical investigation and in accordance with the provisions of Section 1810 and its subparts (§1810, §1810.1–§1810.3) . The design must demonstrate allowable axial and lateral capacities by approved formulas, analysis or load tests, address stability, settlement and group effects, and comply with the specific detailing and minimum dimension rules in §1810.3 .

Requirements in detail

Governing scope and the must-have geotechnical basis

  • Deep foundations must be designed and installed on the basis of a geotechnical investigation as set forth in Section 1803 (see §1810.1.1) — the soils report drives allowable capacities, embedment, special details and tests required .
  • Existing foundation elements left in place cannot be reused without evidence they meet current requirements; they must be load‑tested or redriven and the design load shall be the lowest allowable capacity determined by tests or redriving data (§1810.1.2) .

Analysis (what must be checked)

  • Lateral support / buckling: Soils other than fluid soils are assumed to provide lateral support unless elements stand unbraced in air, water or fluid soils. For unbraced elements the code permits assuming lateral support at a point 5 ft into stiff soil or 10 ft into soft soil unless the building official accepts a project-specific geotechnical justification (§1810.2.1) .
  • Stability and bracing: Groups must be braced so elements are laterally stable; three or more elements in a rigid cap with approximately radial spacing ≥ 60° are considered braced (§1810.2.2) .
  • Settlement: Predicted settlement of single elements or groups must be estimated by an approved method; predicted settlements must not cause harmful distortion, instability or overloading of elements (§1810.2.3) .
  • Lateral load interaction: Moments, shears and lateral deflections must reflect nonlinear soil–structure interaction; if embedment depth / least horizontal dimension ≤ 6 you may model the element as rigid (§1810.2.4) .
  • Group effects: Lateral group effects must be evaluated where spacing (center‑to‑center) in the lateral force direction is < 8× the least horizontal element dimension; axial group effects for spacing < 3× the least horizontal dimension (§1810.2.5) .

Determination of allowable loads (axial & lateral)

  • Allowable axial and lateral loads may be computed by approved formulas, methods of analysis, or by load testing (see §1810.3.3) .
  • Driving criteria: For driven piles evaluated by driving formulas, the allowable compressive load calculated by such formulas shall not exceed 40 tons (356 kN). For allowable loads above 40 tons the wave‑equation driveability analysis is required and allowable loads must be verified by load tests as required (§1810.3.3.1.1) .
  • Load testing: Where design compressive loads exceed allowable stresses or where the load is in doubt, control test elements shall be tested per ASTM D1143 or ASTM D4945; allowable loads from tests shall not exceed one‑half of the ultimate axial capacity as assessed per published methods and must consider settlement tolerances (§1810.3.3.1.2) .
  • Allowable lateral load: When required, lateral capacity must be determined by approved analysis or lateral load tests (ASTM D3966), to at least twice the proposed working design lateral load. The allowable lateral load shall not be more than one‑half of the load producing 1 in gross lateral movement at the lower of top of element or ground surface, unless larger movement is demonstrated harmless (§1810.3.3.2) .

Design and detailing rules (materials, dimensions, reinforcement, seismic)

  • General design: Deep foundations are to be designed and detailed in accordance with §1810.3. Concrete elements supported laterally for their full height and with bending limited to accidental eccentricities may be designed using allowable‑stress ASD combinations in ASCE 7 §2.4; otherwise strength design (ASCE 7 §2.3) is required (§1810.3.1.1) .
  • Mislocation: The foundation/superstructure must account for mislocation of any element by not less than 3 in; to resist mislocations compressive overload to 110% of allowable is permitted (§1810.3.1.3) .
  • Minimum dimensions and length limits:
    • Precast minimum lateral dimension: 8 in (§1810.3.5.1) .
    • Cast‑in‑place or grouted with permanent casing: nominal outside diameter ≥ 8 in (§1810.3.5.2.1) .
    • Uncased cast‑in‑place / grouted‑in‑place: specified diameter ≥ 12 in; element length not to exceed 30× specified diameter unless special supervision and submittal by RDP (§1810.3.5.2.2) .
  • Special elements: Belled and socketed drilled shafts, micropiles, precast piles, helical piles and composite elements have detailed provisions (e.g., socketed shafts require casing to bedrock and rock socket depth at least the casing outside diameter, micropiles must be grouted and carry steel reinforcement, etc.) — see §1810.3.9–§1810.3.10 for specifics .
  • Seismic curvature and detailing: For structures in Seismic Design Categories D–F on Site Class E or F, deep foundations must be able to accommodate maximum imposed curvatures from earthquake motions. Certain detailing exceptions apply (e.g., precast prestressed piles per §1810.3.8, minimum longitudinal reinforcement ratios and ACI 318 detailing for cast‑in‑place elements) (§1810.2.4.1, §1810.3.8) .

Decision‑relevant quick reference table

Criterion / value Typical decision use Code reference
Geotechnical basis required All deep foundation designs must be founded on soils report per Section 1803 §1810.1.1
Lateral support assumption for unbraced elements Consider laterally supported at 5 ft into stiff soil or 10 ft into soft soil unless geotech study says otherwise §1810.2.1
Minimum precast lateral dimension Minimum section dimension = 8 in §1810.3.5.1
Minimum cased cast‑in‑place diameter Nominal outside diameter ≥ 8 in §1810.3.5.2.1
Minimum uncased cast‑in‑place diameter Specified diameter ≥ 12 in; length ≤ 30× diameter (unless special supervision) §1810.3.5.2.2
Max allowable compressive load by driving formula ≤ 40 tons (356 kN); >40 tons requires wave‑equation analysis and verification tests §1810.3.3.1.1
Load test standards Control tests per ASTM D1143 or ASTM D4945 when required §1810.3.3.1.2
Lateral test acceptance Lateral tests per ASTM D3966; allowable ≤ ½ of load producing 1 in gross lateral movement §1810.3.3.2
Group effects — lateral Analyze if spacing < 8× least horizontal element dimension §1810.2.5
Group effects — axial Analyze if spacing < 3× least horizontal element dimension §1810.2.5

Exceptions & special cases

  • Existing piles left in place: may not be used for new support unless sound evidence is provided and they are load‑tested or redriven; design load must be the lowest allowable determined by test/redrive (§1810.1.2) .
  • Isolated large cast‑in‑place elements: an isolated, unbraced cast‑in‑place deep foundation element with least horizontal dimension ≥ 2 ft may be permitted without lateral bracing if the analysis shows adequacy (§1810A.2.2 exceptions as adopted in main text) .
  • Length/diameter exception: an element length exceeding 30× the specified diameter is allowed only under direct supervision of an RDP experienced in deep foundations with a submittal to the building official (§1810.3.5.2.2) .
  • Seismic detailing exceptions: Some precast prestressed piles and cast‑in‑place elements meeting specific reinforcement/detailing requirements are allowed to be deemed compliant with seismic curvature capacity rules (§1810.2.4.1 exceptions, §1810.3.8) .

Common mistakes

  • Relying on assumed capacities without an appropriate geotechnical investigation — the CBC explicitly ties deep foundation design to the soils report (§1810.1.1) .
  • Omitting required load tests when design loads exceed the allowable stresses or when the pile type/installation method makes formula capacities uncertain (§1810.3.3.1.2) .
  • Ignoring group effects for closely spaced piles (axial <3×, lateral <8×) — this can underpredict settlement and lateral demand (§1810.2.5) .
  • Using driven‑pile allowable compressive loads above 40 tons without wave equation driveability analysis and verification tests (§1810.3.3.1.1) .
  • Not detailing for seismic curvature/ductility where required (SDC D–F on Site Class E/F), or failing to follow the ACI/ASCE referenced detailing when invoked (§1810.2.4.1, §1810.3.1.1) .
  • Failing to account for mislocation tolerance (design must consider ±3 in) or not using the permitted 110% compressive overload to guard against mislocation (§1810.3.1.3) .

Worked example — applying the code to a simple drilled‑shaft scenario

Scenario: You are designing cast‑in‑place drilled shafts to support column loads of 90 kips (compression) each; the chosen shaft diameter is 24 in and proposed embedded length in bearing strata is 45 ft. Site is non‑liquefiable. The shafts are uncased shafts (open hole).

Step checks against CBC:

  1. Minimum diameter: Uncased elements must have specified diameter ≥ 12 in — 24 in satisfies §1810.3.5.2.2 .
  2. Length limit: Element length shall not exceed 30× diameter unless special supervision is submitted. 30×24 in = 720 in = 60 ft. Proposed length 45 ft < 60 ft, so within normal limit (§1810.3.5.2.2) .
  3. Allowable axial capacity basis: CBC requires allowable axial loads be determined by approved method, formula or load test (§1810.3.3). If the soils report supplies allowable bearing/friction values and the RDP uses an approved analysis to compute an allowable ≥ 90 kips, design can proceed on that basis; if the computed allowable is close to or below 90 kips, then control load tests per ASTM D1143 or D4945 are required (§1810.3.3.1.2) .
  4. Settlement: Predict settlement by approved analysis and verify predicted settlement does not cause distress or overloading of elements (§1810.2.3) .
  5. Group effects: If shafts are spaced with center‑to‑center spacing less than 3× the least horizontal element dimension (3×24 in = 6 ft) you must evaluate axial group effects; if spacing in the lateral direction is less than 8× (8×24 in = 16 ft) you must evaluate lateral group interaction (§1810.2.5) .
  6. Seismic detailing: If the structure is in SDC D, E or F and the site is Site Class E or F, the RDP must check curvature demands and provide the required reinforcement/detailing or meet the specific exceptions (§1810.2.4.1) .

Actionable conclusion for this example: confirm allowable axial capacity from the geotechnical report and RDP analysis; if capacity computed by standard allowable‑stress methods is uncertain or near the design 90 kips, perform at least one control axial load test per ASTM D1143 and use test results to set allowable ≤ ½ of measured ultimate (with settlement checks) as required by §1810.3.3.1.2 .

Related provisions

  • Soils report / geotechnical investigation — §1803 (referenced by §1810.1.1) .
  • Seismic site classification and design parameters — §1613.2.2 (used in seismic curvature rules for deep foundations) .
  • Load combinations and strength vs. allowable‑stress design — ASCE 7 §§2.3 & 2.4 (referenced by §1810.3.1.1) — see §1810.3.1.1 for the CBC linkage .
  • ACI 318 references for precast and cast‑in‑place detailing (ACI provisions are invoked in §1810.3.8 and §1810.3.9) .
  • ASTM standards cited for tests: ASTM D1143, D4945 (axial load tests) and ASTM D3966 (lateral load tests) — see §1810.3.3.1.2 and §1810.3.3.2 for code requirements .

Code references

Grounded in the retrieved California Building Code — click a citation to read the verbatim passage:

  • CBC § 1810.1 High relevance — show source text

    Exception: Alternate trench locations and pipe clearances shall be permitted when approved by registered design professional and the enforcement agent.

    SECTION 1810—DEEP FOUNDATIONS

    1810.1 General. Deep foundations shall be analyzed, designed, detailed and installed in accordance with Sections 1810.1 through 1810.4.

    1810.1.1 Geotechnical investigation. Deep foundations shall be designed and installed on the basis of a geotechnical investigation as set forth in Section 1803.

    1810.1.2 Use of existing deep foundation elements. Deep foundation elements left in place where a structure has been demolished shall not be used for the support of new construction unless satisfactory evidence is submitted to the building official, which indicates that the elements are sound and meet the requirements of this code. Such elements shall be load tested or redriven to verify their capacities. The design load applied to such elements shall be the lowest allowable load as determined by tests or redriving data.

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    1810.1.3 Deep foundation elements classified as columns. Deep foundation elements standing unbraced in air, water or fluid soils shall be classified as columns and designed as such in accordance with the provisions of this code from their top down to the point where adequate lateral support is provided in accordance with Section 1810.2.1.

    Exception: Where the unsupported height to least horizontal dimension of a cast-in-place deep foundation element does not exceed three, it shall be permitted to design and construct such an element as a pedestal in accordance with ACI 318.

    1810.1.4 Special types of deep foundations. The use of types of deep foundation elements not specifically mentioned herein is permitted, subject to the approval of the building official, upon the submission of acceptable test data, calculations and other information relating to the structural properties and load capacity of such elements. The allowable stresses for materials shall not in any case exceed the limitations specified herein.

    1810.2 Analysis. The analysis of deep foundations for design shall be in accordance with Sections 1810.2.1 through 1810.2.5.

    1810.2.1 Lateral support. Any soil other than fluid soil shall be deemed to afford sufficient lateral support to prevent buckling of deep foundation elements and to permit the design of the elements in accordance with accepted engineering practice and the applicable provisions of this code.

    Where deep foundation elements stand unbraced in air, water or fluid soils, it shall be permitted to consider them laterally supported at a point 5 feet (1524 mm) into stiff soil or 10 feet (3048 mm) into soft soil unless otherwise approved by the building official on the basis of a geotechnical investigation by a registered design professional.

    1810.2.2 Stability. Deep foundation elements shall be braced to provide lateral stability in all directions. Three or more elements connected by a rigid cap shall be considered to be braced, provided that the elements are located in radial directions from the centroid of the group not less than 60 degrees (1 rad) apart. A two-element group in a rigid cap shall be considered to be braced along the axis connecting the two elements. Methods used to brace deep foundation elements shall be subject to the approval of the building official.

  • CBC § 1810.2.4.1 High relevance — show source text

    1810.2.4.1 Seismic Design Categories D through F. For structures assigned to Seismic Design Category D, E or F, deep foundation elements on Site Class E or F sites, as determined in Section 1613.2.2, shall be designed and constructed to withstand maximum imposed curvatures from earthquake ground motions and structure response. Curvatures shall include free-field soil strains modified for soil-foundation-structure interaction coupled with foundation element deformations associated with earthquake loads imparted to the foundation by the structure.

    Exception: Deep foundation elements that satisfy the following additional detailing requirements shall be deemed to comply with the curvature capacity requirements of this section:

    1. Precast prestressed concrete piles detailed in accordance with Section 1810.3.8.
    2. Cast-in-place deep foundation elements with a minimum longitudinal reinforcement ratio of 0.005 extending the full length of the element and detailed in accordance with Sections 18.7.5.2, 18.7.5.3 and 18.7.5.4 of ACI 318 as required by Section 1810.3.9.4.2.2.

    1810.2.5 Group effects. The analysis shall include group effects on lateral behavior where the center-to-center spacing of deep foundation elements in the direction of lateral force is less than eight times the least horizontal dimension of an element. The analysis shall include group effects on axial behavior where the center-to-center spacing of deep foundation elements is less than three times the least horizontal dimension of an element. Group effects shall be evaluated using a generally accepted method of analysis; the analysis for uplift of grouped elements with center-to-center spacing less than three times the least horizontal dimension of an element shall be evaluated in accordance with Section 1810.3.3.1.6.

    1810.3 Design and detailing. Deep foundations shall be designed and detailed in accordance with Sections 1810.3.1 through 1810.3.13.

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    1810.3.1 Design conditions. Design of deep foundations shall include the design conditions specified in Sections 1810.3.1.1 through 1810.3.1.6, as applicable.

    1810.3.1.1 Design methods for concrete elements. Where concrete deep foundations are laterally supported in accordance with Section 1810.2.1 for the entire height and applied forces cause bending moments not greater than those resulting from accidental eccentricities, structural design of the element using the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605.2 and the allowable stresses specified in this chapter shall be permitted. Otherwise, the structural design of concrete deep foundation elements shall use the strength load combinations specified in ASCE 7, Section 2.3 and approved strength design methods.

    1810.3.1.2 Composite elements. Where a single deep foundation element comprises two or more sections of different materials or different types spliced together, each section of the composite assembly shall satisfy the applicable requirements of this code, and the maximum allowable load in each section shall be limited by the structural capacity of that section.

  • CBC § 2.2 High relevance — show source text

    Splices occurring in the upper 10 feet (3048 mm) of the embedded portion of an element shall be designed to resist at allowable stresses the moment and shear that would result from an assumed eccentricity of the axial load of 3 inches (76 mm), or the element shall be braced in accordance with Section 1810 A .2.2 to other deep foundation elements that do not have splices in the upper 10 feet (3048 mm) of embedment.

    1810 A .3.6.1 Seismic Design Categories C through F. For structures assigned to Seismic Design Category C, D, E or F splices of deep foundation elements shall develop the lesser of the following:

    1. The nominal strength of the deep foundation element.
    2. The axial and shear forces and moments from the seismic load effects including overstrength factor in accordance with Section 2.3.6 or 2.4.5 of ASCE 7.

    1810 A .3.7 Top of element detailing at cutoffs. Where a minimum length for reinforcement or the extent of closely spaced confinement reinforcement is specified at the top of a deep foundation element, provisions shall be made so that those specified lengths or extents are maintained after cutoff.

    1810 A .3.8 Precast concrete piles. Precast concrete piles shall be designed and detailed in accordance with ACI 318.

    Exception: Where the axial load from seismic forces is amplified by the applicable overstrength factor, Ω 0 , the axial load limits in Section 18.13.5.10.6 of ACI 318 may be increased by two times.

    1810 A .3.9 Cast-in-place deep foundations. Cast-in-place deep foundation elements shall be designed and detailed in accordance with Sections 1810 A .3.9.1 through 1810 A .3.9.6.

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    1810 A .3.9.1 Design cracking moment. The design cracking moment ( φ M n ) for a cast-in-place deep foundation element not enclosed by a structural steel pipe or tube shall be determined using the following equation:

    Equation 18 A -5

    φ M n = 3 f ′ c S m

    For SI: φ M n = 0.25 f ′ c S m

    where:

    f ′ c = Specified compressive strength of concrete or grout, psi (MPa). S m = Elastic section modulus, neglecting reinforcement and casing, cubic inches (mm [3] ).

    1810 A .3.9.2 Required reinforcement. Where subject to uplift or where the required moment strength determined using the load combinations of ASCE 7, Section 2.3 exceeds the design cracking moment determined in accordance with Section 1810 A .3.9.1, cast-in-place deep foundations not enclosed by a structural steel pipe or tube shall be reinforced. Where reinforcement is required, it shall be in compliance with Chapter 20 of ACI 318.

  • CBC § 1810.3.9.5 High relevance — show source text

    1810.3.9.5 Belled drilled shafts. Where drilled shafts are belled at the bottom, the edge thickness of the bell shall be not less than that required for the edge of footings. Where the sides of the bell slope at an angle less than 60 degrees (1 rad) from the horizontal, the effects of vertical shear shall be considered.

    1810.3.9.6 Socketed drilled shafts. Socketed drilled shafts shall have a permanent pipe or tube casing that extends down to bedrock and an uncased socket drilled into the bedrock, both filled with concrete. Socketed drilled shafts shall have reinforcement or a structural steel core for the length as indicated by an approved method of analysis.

    The depth of the rock socket shall be sufficient to develop the full load-bearing capacity of the element with a minimum safety factor of two, but the depth shall be not less than the outside diameter of the pipe or tube casing. The design of the rock socket is permitted to be predicated on the sum of the allowable load-bearing pressure on the bottom of the socket plus bond along the sides of the socket.

    Where a structural steel core is used, the gross cross-sectional area of the core shall not exceed 25 percent of the gross area of the drilled shaft.

    1810.3.10 Micropiles. Micropiles shall be designed and detailed in accordance with Sections 1810.3.10.1 through 1810.3.10.4.

    1810.3.10.1 Construction. Micropiles shall develop their load-carrying capacity by means of a bond zone in soil, bedrock or a combination of soil and bedrock. Micropiles shall be grouted and have either a steel pipe or tube or steel reinforcement at

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    every section along the length. It shall be permitted to transition from deformed reinforcing bars to steel pipe or tube reinforcement by extending the bars into the pipe or tube section by not less than their development length in tension in accordance with ACI 318.

    1810.3.10.2 Materials. Reinforcement shall consist of deformed reinforcing bars in accordance with ASTM A615 Grade 60 or 75 or ASTM A722 Grade 150.

    The steel pipe or tube shall have a minimum wall thickness of [3] / 16 inch (4.8 mm). Splices shall comply with Section 1810.3.6. The steel pipe or tube shall have a minimum yield strength of 45,000 psi (310 MPa) and a minimum elongation of 15 percent as shown by mill certifications or two coupon test samples per 40,000 pounds (18 160 kg) of pipe or tube.

    1810.3.10.3 Reinforcement. For micropiles or portions thereof grouted inside a temporary or permanent casing or inside a hole drilled into bedrock or a hole drilled with grout, the steel pipe or tube or steel reinforcement shall be designed to carry not less than 40 percent of the design compression load. Micropiles or portions thereof grouted in an open hole in soil without temporary or permanent casing and without suitable means of verifying the hole diameter during grouting shall be designed to carry the entire compression load in the reinforcing steel. Where a steel pipe or tube is used for reinforcement, the portion of the grout enclosed within the pipe is permitted to be included in the determination of the allowable stress in the grout.

  • CBC § 1810.3 High relevance — show source text

    1810.3 Design and detailing. Deep foundations shall be designed and detailed in accordance with Sections 1810.3.1 through 1810.3.13.

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    1810.3.1 Design conditions. Design of deep foundations shall include the design conditions specified in Sections 1810.3.1.1 through 1810.3.1.6, as applicable.

    1810.3.1.1 Design methods for concrete elements. Where concrete deep foundations are laterally supported in accordance with Section 1810.2.1 for the entire height and applied forces cause bending moments not greater than those resulting from accidental eccentricities, structural design of the element using the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605.2 and the allowable stresses specified in this chapter shall be permitted. Otherwise, the structural design of concrete deep foundation elements shall use the strength load combinations specified in ASCE 7, Section 2.3 and approved strength design methods.

    1810.3.1.2 Composite elements. Where a single deep foundation element comprises two or more sections of different materials or different types spliced together, each section of the composite assembly shall satisfy the applicable requirements of this code, and the maximum allowable load in each section shall be limited by the structural capacity of that section.

    1810.3.1.3 Mislocation. The foundation or superstructure shall be designed to resist the effects of the mislocation of any deep foundation element by not less than 3 inches (76 mm). To resist the effects of mislocation, compressive overload of deep foundation elements to 110 percent of the allowable design load shall be permitted.

    1810.3.1.4 Driven piles. Driven piles shall be designed and manufactured in accordance with accepted engineering practice to resist all stresses induced by handling, driving and service loads.

    1810.3.1.5 Helical piles. Helical piles shall be designed and manufactured in accordance with accepted engineering practice to resist all stresses induced by installation into the ground and service loads.

    1810.3.1.5.1 Helical piles seismic requirements. [OSHPD 1R, 2 & 5] For structures assigned to Seismic Design Category D, E or F, capacities of helical piles shall be determined in accordance with Section 1810.3.3 by at least two project specific pre-produc- tion tests for each soil profile, size and depth of helical pile. At least two percent of all production piles shall be proof tested to design strength determined by using load combinations in ASCE 7, Section 2.3.6.

    Helical piles shall satisfy corrosion resistance requirements of ICC-ES AC 358. In addition, all helical pile materials that are subject to corrosion shall include at least [1] / 16 inch corrosion allowance.

    Helical piles shall not be considered as carrying any horizontal loads.

  • CBC § 3.1 High relevance — show source text

    1810 A .3 Design and detailing. Deep foundations shall be designed and detailed in accordance with Sections 1810 A .3.1 through 1810 A .3.13.

    1810 A .3.1 Design conditions. Design of deep foundations shall include the design conditions specified in Sections 1810 A .3.1.1 through 1810 A .3.1.6, as applicable.

    1810 A .3.1.1 Design methods for concrete elements. Where concrete deep foundations are laterally supported in accordance with Section 1810 A .2.1 for the entire height and applied forces cause bending moments not greater than those resulting from accidental eccentricities, structural design of the element using the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605 A .2 and the allowable stresses specified in this chapter shall be permitted. Otherwise, the structural design of concrete deep foundation elements shall use the strength load combinations specified in ASCE 7, Section 2.3 and approved strength design methods.

    1810 A .3.1.2 Composite elements. Where a single deep foundation element comprises two or more sections of different materials or different types spliced together, each section of the composite assembly shall satisfy the applicable requirements of this code, and the maximum allowable load in each section shall be limited by the structural capacity of that section.

    1810 A .3.1.3 Mislocation. The foundation or superstructure shall be designed to resist the effects of the mislocation of any deep foundation element by not less than 3 inches (76 mm). To resist the effects of mislocation, compressive overload of deep foundation elements to 110 percent of the allowable design load shall be permitted.

    1810 A .3.1.4 Driven piles. Driven piles shall be designed and manufactured in accordance with accepted engineering practice to resist all stresses induced by handling, driving and service loads.

    1810 A .3.1.5 Helical piles. Helical piles shall be designed and manufactured in accordance with accepted engineering practice to resist all stresses induced by installation into the ground and service loads.

    1810A.3.1.5.1 Helical piles seismic requirements. For structures assigned to Seismic Design Category D, E or F, capacities of helical piles shall be determined in accordance with Section 1810A.3.3 by at least two project-specific preproduction tests for each soil profile, size and depth of helical pile. At least two percent of all production piles shall be proof tested to the load deter- mined in accordance with Section 1617A.1.15.

    Helical piles shall satisfy corrosion resistance requirements of ICC-ES AC 358. In addition, all helical pile materials that are subject to corrosion shall include at least [1] / 16 -inch corrosion allowance.

    Helical piles shall not be considered as carrying any horizontal loads.

  • CBC § 1812A.4.2 High relevance — show source text

    _ 10. Allowable vertical soil bearing pressure friction resistance, and lateral passive soil resistance for the drilled pier concrete shafts and associated factors of safety for these allowable capacities. 11. Soil-pier shaft/pile interaction assumptions and lateral soil stiffness to be used in design for drilled pier concrete shaft or pile lateral loads.

    12. Acceptable drilling methods. 13. Geotechnical observation and monitoring recommendations.

    1812A.4.2 Structural requirements : 1. Tendons shall be thread-bar anchors conforming to ASTM A722. 2. Anchor design loads shall be based upon the load combinations in Section 2.4 of ASCE 7 and shall not exceed 60 percent of the specified minimum tensile strength of the tendons. 3. The anchor shall be designed to fail in grout bond to the soil or rock before pullout of the soil wedge.

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    4. Design of shoring system shall account for as-built locations of soil anchors considering all specified construction tolerances in Section 1812A.8.

    5. Design of shoring system shall account for both short and long-term deformation.

    1812A.4.3 Testing of tie-back anchors : 1. The geotechnical engineer shall keep a record at job site of all test loads, total anchor movement, and report their accuracy. 2. The shoring design engineer shall specify design loads for each anchor.

    1812A.5 Construction. The construction procedure shall address the following: 1. Holes drilled for piles/tie-back anchors shall be done without detrimental loss of ground, sloughing or caving of materials and without endangering previously installed shoring members or existing foundations. 2. Drilling of earth anchor shafts for tie-backs shall occur when the drill bench reaches two to three feet below the level of the tie- back pockets. 3. Casing or other methods shall be used where necessary to prevent loss of ground and collapse of the hole. 4. The drill cuttings from earth anchor shaft shall be removed prior to anchor installation. 5. Unless tremie methods are used, all water and loose materials shall be removed from the holes prior to installing piles/tie- backs.

    6. Tie-back anchor rods with attached centralizing devices shall be installed into the shaft or through the drill casing. Centralizing device shall not restrict movement of the grout. 7. After lagging installation, voids between lagging and soil shall be backfilled immediately to the full height of lagging. 8. The soldier piles shall be placed within specified tolerances in the drilled hole and braced against displacement during grout- _ing. Shafts shall be filled with concrete up to the elevation shown on the construction documents.

  • CBC § 1810.3.8 High relevance — show source text

    1810.3.8 Precast concrete piles. Precast concrete piles shall be designed and detailed in accordance with ACI 318.

    Exceptions:

    1. For precast prestressed piles in Seismic Design Category C, the minimum volumetric ratio of spirals or circular hoops required by Section 18.13.5.10.4 of ACI 318 shall not apply in cases where the design includes full consideration of load combinations specified in ASCE 7, Section 2.3.6 or Section 2.4.5 and the applicable overstrength factor, Ω 0 . In such cases, minimum transverse reinforcement index shall be as specified in Section 13.4.5.6 of ACI 318. [OSHPD 1R, 2 & 5] not permitted by OSHPD.
    2. For precast prestressed piles in Seismic Design Categories D through F and in Site Class A, B, BC, C, CD, D or DE sites, the minimum volumetric ratio of spirals or circular hoops required by Section 18.13.5.10.5(c) of ACI 318 shall not apply in cases where the design includes full consideration of load combinations specified in ASCE 7, Section 2.3.6 or Section 2.4.5 and the applicable overstrength factor, Ω 0 . In such cases, minimum transverse reinforcement shall be as specified in Section 13.4.5.6 of ACI 318. [OSHPD 1R, 2 & 5] not permitted by OSHPD.

    [OSHPD 1R, 2 & 5] Exception: Where the axial load from seismic forces is amplified by the applicable overstrength factor, Ω 0 , the axial load limits in Section 18.13.5.10.6 of ACI 318 may be increased by two times.

    1810.3.9 Cast-in-place deep foundations. Cast-in-place deep foundation elements shall be designed and detailed in accordance with Sections 1810.3.9.1 through 1810.3.9.6.

    1810.3.9.1 Design cracking moment. The design cracking moment ( φ M n ) for a cast-in-place deep foundation element not enclosed by a structural steel pipe or tube shall be determined using the following equation:

    18-26 2025 CALIFORNIA BUILDING CODE

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    SOILS AND FOUNDATIONS

    Equation 18-5

    φ M n = 3 f ′ c S m

    For SI: φ M n = 0.25 f ′ c S m

    where:

    f ′ c = Specified compressive strength of concrete or grout, psi (MPa). S m = Elastic section modulus, neglecting reinforcement and casing, cubic inches (mm [3] ).

  • CBC § 2.4 High relevance — show source text

    1810 A .2.4 Lateral loads. The moments, shears and lateral deflections used for design of deep foundation elements shall be established considering the nonlinear interaction of the shaft and soil, as determined by a registered design professional. Where the ratio of the depth of embedment of the element to its least horizontal dimension is less than or equal to six, it shall be permitted to assume the element is rigid.

    1810 A .2.4.1 Seismic Design Categories D through F. For structures assigned to Seismic Design Category D, E or F, deep foundation elements on Site Class E or F sites, as determined in Section 1613 A .2.2, shall be designed and constructed to withstand maximum imposed curvatures from earthquake ground motions and structure response. Curvatures shall include free-field soil strains modified for soil-foundation-structure interaction coupled with foundation element deformations associated with earthquake loads imparted to the foundation by the structure.

    Exception: Deep foundation elements that satisfy the following additional detailing requirements shall be deemed to comply with the curvature capacity requirements of this section:

    1. Precast prestressed concrete piles detailed in accordance with Section 1810 A .3.8.
    2. Cast-in-place deep foundation elements with a minimum longitudinal reinforcement ratio of 0.005 extending the full length of the element and detailed in accordance with Sections 18.7.5.2, 18.7.5.3 and 18.7.5.4 of ACI 318 as required by Section 1810 A .3.9.4.2.2.

    1810 A .2.5 Group effects. The analysis shall include group effects on lateral behavior where the center-to-center spacing of deep foundation elements in the direction of lateral force is less than eight times the least horizontal dimension of an element. The analysis shall include group effects on axial behavior where the center-to-center spacing of deep foundation elements is less than three times the least horizontal dimension of an element. Group effects shall be evaluated using a generally accepted method of analysis; the analysis for uplift of grouped elements with center-to-center spacing less than three times the least horizontal dimension of an element shall be evaluated in accordance with Section 1810 A .3.3.1.6.

    1810 A .3 Design and detailing. Deep foundations shall be designed and detailed in accordance with Sections 1810 A .3.1 through 1810 A .3.13.

    1810 A .3.1 Design conditions. Design of deep foundations shall include the design conditions specified in Sections 1810 A .3.1.1 through 1810 A .3.1.6, as applicable.

    1810 A .3.1.1 Design methods for concrete elements. Where concrete deep foundations are laterally supported in accordance with Section 1810 A .2.1 for the entire height and applied forces cause bending moments not greater than those resulting from accidental eccentricities, structural design of the element using the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605 A .2 and the allowable stresses specified in this chapter shall be permitted. Otherwise, the structural design of concrete deep foundation elements shall use the strength load combinations specified in ASCE 7, Section 2.3 and approved strength design methods.

  • CBC § 12.13 High relevance — show source text

    Exception: Grade beams not subject to differential settlement exceeding one-fourth of the thresholds specified in ASCE 7 Table 12.13-3 and designed to resist the seismic load effects including overstrength factor in accordance with Section 2.3.6 or 2.4.5 of ASCE 7 need not comply with ACI 318 Section 18.13.3.1.

    1809A.15 Pipes and trenches. Unless otherwise recommended by the soils report, open or backfilled trenches parallel with a footing shall not be below a plane having a downward slope of 1 unit vertical to 2 units horizontal (50 percent slope) from a line 9 inches (229 mm) above the bottom edge of the footing, and not closer than 18 inches (457 mm) from the face of such footing.

    Where pipes cross under footings, the footings shall be specially designed. Pipe sleeves shall be provided where pipes cross through footings or footing walls and sleeve clearances shall provide for possible footing settlement, but not less than 1 inch (25 mm) all around pipe.

    Exception: Alternate trench locations and pipe clearances shall be permitted when approved by registered design professional and the enforcement agent.

    SECTION 1810 A —DEEP FOUNDATIONS

    1810 A .1 General. Deep foundations shall be analyzed, designed, detailed and installed in accordance with Sections 1810 A .1 through 1810 A .4.

    1810 A .1.1 Geotechnical investigation. Deep foundations shall be designed and installed on the basis of a geotechnical investigation as set forth in Section 1803 A .

    1810 A .1.2 Use of existing deep foundation elements. Deep foundation elements left in place where a structure has been demolished shall not be used for the support of new construction unless satisfactory evidence is submitted to the building official, which indicates that the elements are sound and meet the requirements of this code. Such elements shall be load tested or redriven to verify their capacities. The design load applied to such elements shall be the lowest allowable load as determined by tests or redriving data.

    1810 A .1.3 Deep foundation elements classified as columns. Deep foundation elements standing unbraced in air, water or fluid soils shall be classified as columns and designed as such in accordance with the provisions of this code from their top down to the point where adequate lateral support is provided in accordance with Section 1810 A .2.1.

    Exception: Where the unsupported height to least horizontal dimension of a cast-in-place deep foundation element does not exceed three, it shall be permitted to design and construct such an element as a pedestal in accordance with ACI 318.

    1810 A .1.4 Special types of deep foundations. The use of types of deep foundation elements not specifically mentioned herein is permitted, subject to the approval of the building official, upon the submission of acceptable test data, calculations and other information relating to the structural properties and load capacity of such elements. The allowable stresses for materials shall not in any case exceed the limitations specified herein.

    1810 A .2 Analysis. The analysis of deep foundations for design shall be in accordance with Sections 1810 A .2.1 through 1810 A .2.5.

  • CBC § 1810.3.3.1.2. High relevance — show source text
    1. Ultimate capacity determined from well-documented correlations with installation torque.
    2. Ultimate capacity determined from load tests where required by Section 1810.3.3.1.2. [OSHPD 1R, 2 & 5] Load tests are required to determine the ultimate capacity.
    3. Ultimate axial capacity of pile shaft.
    4. Ultimate axial capacity of pile shaft couplings.
    5. Sum of the ultimate axial capacity of helical bearing plates affixed to pile.

    1810.3.3.2 Allowable lateral load. Where required by the design, the lateral load capacity of a single deep foundation element or a group thereof shall be determined by an approved method of analysis or by lateral load tests to not less than twice the proposed design working load. The resulting allowable lateral load shall not be more than one-half of the load that produces a gross lateral movement of 1 inch (25 mm) at the lower of the top of the foundation element and the ground surface, unless it can be shown that the predicted lateral movement shall cause neither harmful distortion of, nor instability in, the structure, nor cause any element to be loaded beyond its capacity. Group effects shall be evaluated where required by Section 1810.2.5.

    1810.3.4 Subsiding soils or strata. Where deep foundation elements are installed through subsiding soils or other subsiding strata and derive support from underlying firmer materials, consideration shall be given to the downward frictional forces potentially imposed on the elements by the subsiding upper strata.

    Where the influence of subsiding soils or strata is considered as imposing loads on the element, the allowable stresses specified in this chapter shall be permitted to be increased where satisfactory substantiating data are submitted.

    1810.3.5 Dimensions of deep foundation elements. The dimensions of deep foundation elements shall be in accordance with Sections 1810.3.5.1 through 1810.3.5.3, as applicable.

    1810.3.5.1 Precast. The minimum lateral dimension of precast concrete deep foundation elements shall be 8 inches (203 mm). Corners of square elements shall be chamfered.

    1810.3.5.2 Cast-in-place or grouted-in-place. Cast-in-place and grouted-in-place deep foundation elements shall satisfy the requirements of this section.

    1810.3.5.2.1 Cased. Cast-in-place or grouted-in-place deep foundation elements with a permanent casing shall have a nominal outside diameter of not less than 8 inches (203 mm).

    1810.3.5.2.2 Uncased. Cast-in-place or grouted-in-place deep foundation elements without a permanent casing shall have a specified diameter of not less than 12 inches (305 mm). The element length shall not exceed 30 times the specified diameter.

    Exception: The length of the element is permitted to exceed 30 times the specified diameter, provided that the design and installation of the deep foundations are under the direct supervision of a registered design professional knowledgeable in the field of soil mechanics and deep foundations. The registered design professional shall submit a report to the building official stating that the elements were installed in compliance with the approved construction documents.

    1810.3.5.2.3 Micropiles. Micropiles shall have a nominal diameter of 12 inches (305 mm) or less. The minimum diameter set forth elsewhere in Section 1810.3.5 shall not apply to micropiles.

    1810.3.5.3 Steel. Steel deep foundation elements shall satisfy the requirements of this section.

  • CBC § 18A-18 High relevance — show source text

    18A-18 2025 CALIFORNIA BUILDING CODE

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    SOILS AND FOUNDATIONS

    Where the deep foundation elements in the group are placed at a center-to-center spacing less than three times the least horizontal dimension of the largest single element, the allowable uplift load for the group is permitted to be calculated as the lesser of:

    1. The proposed individual allowable uplift load times the number of elements in the group.
    2. Two-thirds of the effective weight of the group and the soil contained within a block defined by the perimeter of the group and the length of the element, plus two-thirds of the ultimate shear resistance along the soil block.

    1810 A .3.3.1.7 Load-bearing capacity. Deep foundation elements shall develop ultimate load capacities of not less than twice the design working loads in the designated load-bearing layers. Analysis shall show that soil layers underlying the designated load-bearing layers do not cause the load-bearing capacity safety factor to be less than two.

    1810 A .3.3.1.8 Bent deep foundation elements. The load-bearing capacity of deep foundation elements discovered to have a sharp or sweeping bend shall be determined by an approved method of analysis or by load testing a representative element.

    1810 A .3.3.1.9 Helical piles. The allowable axial design load, P a, of helical piles shall be determined as follows:

    Equation 18 A -4 P a = 0.5 P u

    where P u is the least value of:

    1. Base capacity plus shaft resistance of the helical pile. The base capacity is equal to the sum of the areas of the helical bearing plates times the ultimate bearing capacity of the soil or rock comprising the bearing stratum. The shaft resistance is equal to the area of the shaft above the uppermost helical bearing plate times the ultimate skin resistance.

    2. Ultimate capacity determined from well-documented correlations with installation torque.

    3. Ultimate capacity determined from load tests.

    4. Ultimate axial capacity of pile shaft.

    5. Ultimate axial capacity of pile shaft couplings.

    6. Sum of the ultimate axial capacity of helical bearing plates affixed to pile.

    1810 A .3.3.2 Allowable lateral load. Where required by the design, the lateral load capacity of a single deep foundation element or a group thereof shall be determined by an approved method of analysis or by lateral load tests in accordance with ASTM D3966 to not less than twice the proposed design working load. The resulting allowable lateral load shall not be more than one-half of the load that produces a gross lateral movement of 1 inch (25 mm) at the lower of the top of the foundation element and the ground surface, unless it can be shown that the predicted lateral movement shall cause neither harmful distortion of, nor instability in, the structure, nor cause any element to be loaded beyond its capacity. Group effects shall be evaluated where required by Section 1810 A .2.5.

    1810 A .3.4 Subsiding soils or strata. Where deep foundation elements are installed through subsiding soils or other subsiding strata and derive support from underlying firmer materials, consideration shall be given to the downward frictional forces potentially imposed on the elements by the subsiding upper strata.

Frequently asked questions

When is a load test required for a pile or drilled shaft?

Load tests are required where design compressive loads exceed those determined using the allowable stresses in the code, where the design load is in doubt, or for certain cast‑in‑place enlarged bases or nonstandard installation methods; control elements shall be tested per ASTM D1143 or D4945 and allowable loads from tests are limited per §1810.3.3.1.2 .

Can I use an existing pile left in place from a demolished structure?

Only if satisfactory evidence is submitted to the building official showing the element is sound and meets code requirements; such elements must be load tested or redriven and the design load must be the lowest allowable indicated by tests or redriving data (§1810.1.2) .

What minimum diameter can I use for an uncased cast‑in‑place shaft?

An uncased cast‑in‑place or grouted‑in‑place element must have a specified diameter of at least 12 inches (§1810.3.5.2.2) .

How does the code handle pile groups spaced closely together?

The code requires analysis of group lateral behavior where center‑to‑center spacing in the lateral direction is less than 8× the least horizontal element dimension and axial group effects where spacing is less than 3× that dimension (§1810.2.5) .

Is there a cap on allowable compressive load from driving formulas?

Yes — allowable compressive load for driven elements determined by driving formulas shall not exceed 40 tons (356 kN); above that the wave‑equation method and verification tests are required (§1810.3.3.1.1) .

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